On 2016/3/26 3:22, Andrew Morton wrote:
> On Fri, 25 Mar 2016 14:56:04 +0800 Xishi Qiu <qiuxishi@xxxxxxxxxx> wrote:
>
>> It is incorrect to use next_node to find a target node, it will
>> return MAX_NUMNODES or invalid node. This will lead to crash in
>> buddy system allocation.
>>
>> ...
>>
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -289,11 +289,11 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private,
>> * now as a simple work-around, we use the next node for destination.
>> */
>> if (PageHuge(page)) {
>> - nodemask_t src = nodemask_of_node(page_to_nid(page));
>> - nodemask_t dst;
>> - nodes_complement(dst, src);
>> + int node = next_online_node(page_to_nid(page));
>> + if (node == MAX_NUMNODES)
>> + node = first_online_node;
>> return alloc_huge_page_node(page_hstate(compound_head(page)),
>> - next_node(page_to_nid(page), dst));
>> + node);
>> }
>>
>> if (PageHighMem(page))
>
> Indeed. Can you tell us more about this circumstances under which the
> kernel will crash? I need to decide which kernel version(s) need the
> patch, but the changelog doesn't contain the info needed to make this
> decision (it should).
>
Hi Andrew,
I read the code v4.4, and find the following path maybe trigger the bug.
alloc_migrate_target()
alloc_huge_page_node() // the node may be offline or MAX_NUMNODES
__alloc_buddy_huge_page_no_mpol()
__alloc_buddy_huge_page()
__hugetlb_alloc_buddy_huge_page()
alloc_pages_node()
__alloc_pages_node()
VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
VM_WARN_ON(!node_online(nid));
Thanks,
Xishi Qiu
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